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agui-cross-sdk-parity

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Keep the AG-UI .NET SDK at feature and wire-format PARITY with the canonical reference SDKs (TypeScript is the source of truth; Python is types/encoder only). USE FOR: porting a feature/event/behavior that landed in the TS (or Python) SDK into .NET, verifying the .NET wire format (JSON, SSE, protobuf) matches the reference, locating where the reference implementation and compatibility fixtures live, mapping a TS concept to the .NET event/client/encoder model, resolving an upstream protocol fix (e.g. a Microsoft.Extensions.AI / Microsoft Agent Framework issue) that needs a .NET counterpart, deciding which .NET package owns a change. DO NOT USE FOR: the mechanics of writing a specific test (use agui-dotnet-unit-tests for serialization round-trips, agui-dotnet-integration-tests for cross-language / E2E harness mechanics, agui-dotnet-wire-types for JSON/proto type rules, agui-dotnet-transport for SSE/HTTP transport details). This skill is about the PARITY PROCESS and where the reference lives, not test authoring.

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AG-UI Cross-SDK Parity

The .NET SDK implements an upstream, multi-language protocol. This skill encodes the parity process: which SDK is authoritative, where its reference and fixtures live, how to map reference concepts onto the .NET model, and how parity is guarded.

Parity Principle

  • TypeScript is canonical for wire format AND client run-loop behavior. When two SDKs disagree, match TS.
  • Python is types + encoder only. It has core (types/events) and an encoder, but no client run-loop and no protobuf (sdks/python/ag_ui/ has core/ and encoder/ but no client/ or proto/). Use it only as a secondary check on type/JSON shape — never for run-loop or proto questions.
  • Upstream protocol or SDK fixes (in the TS client run-loop, or in Microsoft.Extensions.AI / Microsoft Agent Framework) sometimes need a .NET counterpart; treat the TypeScript change as the contract to match.

Where the Reference Lives

ConcernTypeScript reference (source of truth).NET package it maps to
Event & type definitionssdks/typescript/packages/core/src/events.ts, types.ts, event-factories.tssdks/dotnet/src/AGUI.Abstractions/Events/, Messages/
Client run-loop / transportsdks/typescript/packages/client/src/run/, apply/, agent/, transform/sdks/dotnet/src/AGUI.Client/ (AGUIChatClient.cs, AGUIHttpTransport.cs, EventStreamConverter.cs, ToolCallBuilder.cs)
SSE / JSON wire framingsdks/typescript/packages/encoder/src/encoder.tssdks/dotnet/src/AGUI.Formatting/, AGUI.Abstractions/Serialization/
Protobuf wire formatsdks/typescript/packages/proto/src/proto/events.proto, types.proto, patch.protosdks/dotnet/src/AGUI.Protobuf/ (ProtoEventMapper.cs, ProtoMessageMapper.cs)

The src/ packages are AGUI.Abstractions, AGUI.Formatting, AGUI.Protobuf, AGUI.Client, AGUI.Server; sdks/dotnet/AGENTS.md and docs/architecture.md are the canonical description of the layout and conventions.

Porting Workflow

  1. Locate the feature in TS. Find the change in packages/core (a new event/type), packages/client (run-loop / event-application behavior), or packages/proto+encoder (wire framing). Read the TS implementation and its tests to capture the exact contract — field names, ordering, optionality, coalescing rules.
  2. Identify the wire contract. Determine the JSON shape, the proto schema impact (if any), and whether client run-loop state changes. Cross-check the JSON property names against packages/core/src/events.ts.
  3. Map to the .NET model and the right package (table above). Events/types → AGUI.Abstractions; run-loop → AGUI.Client; SSE/JSON framing → AGUI.Formatting; protobuf → AGUI.Protobuf. Follow the .NET conventions in AGENTS.md (one class per file, sealed, source-generated JSON context, PublicAPI.Unshipped.txt).
  4. Implement the .NET change. For a new event, follow the "Adding a new event type" checklist in AGENTS.md (class in Events/, AGUIEventTypes constant, [JsonSerializable], BaseEventJsonConverter case, PublicAPI entry).
  5. Add parity assets (see next section): a TS-produced JSON fixture under tests/AGUI.Abstractions.UnitTests/Compatibility/ and/or a cross-language test in tests/CrossLanguage.Vitest/tests/.
  6. Verify byte/semantic parity — run the compatibility and cross-language tests.
  7. Update docs. Refresh sdks/dotnet/AGENTS.md, docs/architecture.md, and docs/cross-language-testing.md if the change alters the model, package layout, or the set of wire-supported events.

How Parity Is Guarded

Three independent layers catch drift; add to whichever layer the change touches.

  • Compatibility fixtures (catch JSON drift). tests/AGUI.Abstractions.UnitTests/Compatibility/ holds TS-produced JSON fixtures (*-events.json) loaded via FixtureLoader and deserialized into .NET types ({Category}CompatibilityTest.cs, e.g. RunEventsCompatibilityTest, ToolCallEventsCompatibilityTest). A new/changed event shape needs a fixture entry.
  • Cross-language tests (catch end-to-end drift). The harness in tests/CrossLanguage.TestServer/ (C# server) and tests/CrossLanguage.Vitest/ (TS client driving it) proves real interop — see sdks/dotnet/docs/cross-language-testing.md. Scenario specs live in tests/CrossLanguage.Vitest/tests/ (e.g. parallel-tool-calls.test.ts, state-events.test.ts, protobuf-parity.test.ts).
  • Protobuf byte-parity tests. protobuf-parity.test.ts plus tests/AGUI.Protobuf.UnitTests/ verify the binary encoding matches the TS proto output.

Known Parity Boundary: Proto Is a Subset

The protobuf schema covers a subset of events by design. .NET-only events (Reasoning*, Activity*, ToolCallResult) are not in the proto wire format and throw NotSupportedException when mapped — see ProtoEventMapper.cs (the default case lists the 16 supported events: RUN_STARTED/FINISHED/ERROR, STEP_STARTED/FINISHED, TEXT_MESSAGE_START/CONTENT/END, TOOL_CALL_START/ARGS/END, STATE_SNAPSHOT/DELTA, MESSAGES_SNAPSHOT, RAW, CUSTOM) and ProtoMessageMapper.cs. This is a deliberate, documented boundary — do not "fix" it by inventing proto messages that don't exist in events.proto. JSON/SSE remains the full-fidelity wire; protobuf is the constrained one.

Critical Anti-patterns

  1. Never treat .NET as the source of truth. If the .NET behavior differs from TS, the .NET side is the candidate for change — confirm against packages/core / packages/client first.
  2. Never consult Python for run-loop or proto parity. Python has neither. Use it only as a type/JSON cross-check.
  3. Never add a proto mapping for a .NET-only event (Reasoning*, Activity*, ToolCallResult). The NotSupportedException is intentional.
  4. Never land a wire change without a parity asset. A JSON-shape change needs a Compatibility fixture; an interop/behavioral change needs a cross-language test.

Routing to Sibling Skills

This skill governs what to port and where the reference is — delegate test mechanics:

  • agui-dotnet-unit-tests — serialization round-trips and Compatibility fixture tests.
  • agui-dotnet-integration-tests — cross-language / E2E harness (TestServer + Vitest).
  • agui-dotnet-wire-types — JSON/proto type and serialization-context rules.
  • agui-dotnet-transport — SSE / HTTP transport details.